My first reaction was this is a terrible idea, because as soon as you put any focus on ANYTHING other than the target, you will usually miss. Your eye can only focus on one thing, and as soon as your eye focuses on anything else (like a bead or a sight) it disrupts your natural eye-hand coordination. This is why people tell you never to aim a shotgun at a moving target. You can learn to “aim” like this to hit predictable targets like on a skeet or trap range, and it might be an asset for folks with an eye-dominance problem who need to close an eye otherwise, but in general any kind of aiming—even a shotgun bead—will prevent you from being a good wingshooter. That said, I was curious and went looking, as I know holographic sights are a bit different. It seems there is at least 1 reasonably well known shooter using them, although I found several statements about him using the dot as part of dealing with vision problems like cross eye dominance or shifting eye dominance or something along those lines. Hard to tell what the real story is, as all of the info I found was related to paid/sponsored shooters or marketing hype.
Personally, I think the most telling thing is that in competitive circles really no one is using them. If they were helpful for most people, more people would be using them. Until I hear a known-good shooting coach who addresses target focus in an explanation of why this is an asset, either in general or for specific cases, Id personally avoid it.